Along with the recent trend of higher speed and higher performance of vehicles, the tires are required to be improved steering stability, especially, the straight-forward stability in high speed running, gripping performance and break-away controllability in cornering, both on dry and wet road surfaces. And accordingly, hitherto, the double crown radius profile has been selected as the tread surface contour.
In the conventional double crown radial tire, however, although the steering wheel response and road surface gripping performance are somewhat enhanced when running straight or at the initial moment of turning, the limit performance in cornering, for example, breakaway controllability, is not improved sufficiently.
The breakaway, in this case, refers to a phenomenon that the tire skids and escapes from the cornering locus as the cornering force generated on the ground contact surface becomes insufficient against the centrifugal force by the slip angle of cornering. And this is considered to occur, as shown in FIG. 8, when the cornering force CF which has been increased approximately in proportion to the slip angle .alpha. in the small slip angle range decreases its increasing rate gradually in the large slip angle range.